1. Field of the Invention
This disclosure relates to semiconductor devices that include a crystalline layer of silicon or silicon nitride formed between dielectric layers and methods of forming such devices.
2. Description of Related Art
Thin deposited dielectric films are often used to isolate conductors and semiconductors in many different applications. These dielectric films are subjected to breakdown due to diffusion, electromigration or other phenomena. A need exists to create an improved dielectric barrier between conductors or layers in semiconductor components, such as integrated circuits.
Application of high electric fields across insulating films can sometimes lead to local destruction of the material, a phenomenon known as dielectric breakdown. Dielectric materials such as silicon oxides are widely used in the manufacture of semiconductor devices. These materials find use not only as final passivation coatings for completed devices but also as intermediate insulating layers for multi-layer devices.
The continuing trend of scaling down integrated circuits has forced the semiconductor industry to adopt new and improved techniques for fabricating precise dielectric components. One area of concern relates to dielectric layers in the creation of cell capacitors. The expansion of the memory capacity is dependent on the ability to fabricate smaller cells having increased capacities. As such, the thinner a dielectric layer can be manufactured having an equivalent or increased dielectric constant, the smaller the cell. Smaller cells allow an increased density, thereby increasing chip capacity.
Recent improvements in the creation of dielectric films has resulted in higher deposition rates, improved thickness uniformity, better step coverage, lower particle density and fewer pinhole defects which can cause catastrophic failures in semiconductor devices. However, the need to further reduce chip size and improve reliability still exists.
Silicon dioxide is known to have a high defect density especially in thinner dielectric films. Silicon dioxide also exhibits poor characteristics as a diffusion barrier against impurities. Further, silicon dioxide has a relatively low dielectric constant.
In light of silicon dioxide's limitations for dielectric layers, several alternatives have been developed. One such alternative is the use of silicon nitride (Si.sub.3 N.sub.4) as a dielectric layer. This layer can be formed on a substrate's surface through a process which includes Rapid Thermal Nitridation (RTN). Under RTN, the silicon substrate is exposed to either pure ammonia (NH.sub.3) or an ammonia plasma at temperatures approximately between 850 degrees C and 1200 degrees C to form a silicon nitride film.
Dielectric layers fabricated employing RTN, however, have several shortcomings. Conventional RTN-type dielectrics sometimes lack uniformity in their overall composition. Further, conventional RTN-type dielectrics may have questionable reliability in part because of their susceptibility to high electrical leakage, as well as electrical and thermal breakdown. Hence the overall cell capacitance is limited. Therefore, a need exists for an improved dielectric layer less susceptible to current leakage and dielectric breakdown failures. A need also exists for reducing the thickness of the dielectric layer for capacitors. This would result in smaller memory chips, for example.
In addition to seeking out improved dielectric layers, the semiconductor industry has sought out techniques for forming a semiconductor layer on top of a dielectric layer. There are advantages in having this capability. One example is the widespread interest for thin film transistor devices. If possible, an additional layer of transistors could be placed on a chip, providing a more efficient use of space.